Input / output devices Flashcards
What are the two different types of bar codes?
Linear and quick response (QR)
What are the four different types of bar code readers?
Pen-type, laser scanners, CCD readers, and camera-based.
How does a pen-type reader work?
A light source and photo diode are placed next to each other in the tip of a pen. The pen is dragged across the barcode and reads it.
They have a simple design, which makes them cheap and durable. However, they must touch the barcode to be used.
How does a laser-scanner type reader work?
Same as pen type except it uses a laser beam as a light source.
How do charge-coupled device (CCD) readers work?
Uses an array of hundreds of tiny light sensors lined up in a row. The barcode is placed in front of them and they read it.
How do camera-based readers work?
It simply takes a picture of the barcode which is then decoded.
How does a digital camera work?
It uses a CCD or CMOS (complementary metal oxide semiconductor) comprised of millions of tiny light sensors. When the shutter opens, each sensor records the colour and brightness of each pixel, and turns this into a digital signal to be stored.
How do radio frequency identification (RFID) devices work?
The RFID chip consists of a small transponder which stores information, and an antenna. When it receives a signal, the data are transmitted through the antenna.
How does a laser printer work?
Millions of bytes (characters) of data stream into the printer from your computer.
An electronic circuit in the printer (effectively, a small computer in its own right) figures out how to print this data so it looks correct on the page.
The electronic circuit activates the corona wire. This is a high-voltage wire that gives a static electric charge to anything nearby.
The corona wire charges up the photoreceptor drum so the drum gains a positive charge spread uniformly across its surface.
At the same time, the circuit activates the laser to make it draw the image of the page onto the drum. The laser beam doesn’t actually move: it bounces off a moving mirror that scans it over the drum. Where the laser beam hits the drum, it erases the positive charge that was there and creates an area of negative charge instead. Gradually, an image of the entire page builds up on the drum: where the page should be white, there are areas with a positive charge; where the page should be black, there are areas of negative charge.
An ink roller touching the photoreceptor drum coats it with tiny particles of powdered ink (toner). The toner has been given a positive electrical charge, so it sticks to the parts of the photoreceptor drum that have a negative charge (remember that opposite electrical charges attract in the same way that opposite poles of a magnet attract). No ink is attracted to the parts of the drum that have a positive charge. An inked image of the page builds up on the drum.
A sheet of paper from a hopper on the other side of the printer feeds up toward the drum. As it moves along, the paper is given a strong positive electrical charge by another corona wire.
When the paper moves near the drum, its positive charge attracts the negatively charged toner particles away from the drum. The image is transferred from the drum onto the paper but, for the moment, the toner particles are just resting lightly on the paper’s surface.
The inked paper passes through two hot rollers (the fuser unit). The heat and pressure from the rollers fuse the toner particles permanently into the fibres of the paper.
The printout emerges from the side of the copier. Thanks to the fuser unit, the paper is still warm. It’s literally hot off the press!
What could an RFID or bar code be used for?
Shops, for identifying products quickly.
